There may be new hope for patients suffering from limb loss. A new control system pioneered by Todd A. Kuiken, M.D., Ph.D., a professor at Northwestern University and physiatrist at the Rehabilitation Institute of Chicago, allows fine manipulation of prosthetic arms and suggests that even more control is possible.

Targeted muscle reinnervation (TMR) allows prosthesis to respond directly to the brain's signaling, rather than relying on muscle movements like in typical prosthetics. Kuiken came up with the idea for TMR as a graduate student in the 1980s. Rather than learning to control muscle groups in the chest, patients who have undergone TMR simply think of opening their hand, and the hand on the prosthetic opens.

TMR works by rerouting the remaining nerves from the amputated limb to muscles in the chest. Instead of controlling the chest muscles, when a patient wants to grasp something with his hand, the signals from the rerouted nerves cause the muscles in the chest to flex. An electromyogram picks up the electrical signals from the muscle's contraction, and sends it to a microprocessor in the prosthesis. The processor decodes the signal and moves the limb in the intended manner.

So far the system is capable of opening and closing a hand, and bending and straightening an elbow. The microprocessor can be programmed for more signals and further research being done on 16 different movements in the arm and hand promises more range of movement than just the elbow and hand. Fine hand movements such as grasping a pen or tool are not out of the question.

Kuiken and colleagues have also begun work with the military to help soldiers have lost limbs. Brooke Army Medical Center and the Walter Reed Army Hospital are actively involved in the project.

"We're excited to move forward in doing this surgery with our soldiers some day. We've been able to demonstrate remarkable control of artificial limbs and it's an exciting neural machine interface that provides a lot of hope," Kuiken said of the project.

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